1. Field of the Invention
This invention relates to an improved apparatus for growing a vapor phase layer on a semiconductor substrate.
2. Description of the Related Art
A vapor-phase growing apparatus incorporating a high-frequency induction heater is generally employed for depositing a MOCVD (Metal Organic Chemical Vapor Deposition) layer on a semiconductor substrate of III-V group compound such as a GaAs.
FIG. 1 shows such a conventional vapor-phase growing apparatus. A housing 1 houses a reaction tube 2, a coil 3 for high-frequency induction heating, and an elevator 4. The reaction tube 2 is formed of quartz, and provided with an introduction pipe 2A connected to a gas-supply apparatus, not shown, for introducing gas from the supply apparatus into the tube 2. The coil 3 is wound around the reaction tube 2, and connected to the elevator 4, thereby to be moved up and down. The elevator 4 is connected to one end of each of two cables 5, which are connected to a high-frequency generator 6 at the other end. The cables 5, extending between the housing 1 and generator 6, are covered with a safe cover 7.
FIG. 2 shows an essential part of the reaction tube 2. A susceptor 8 formed of carbon is arranged in the tube 2, for supporting a GaAs semiconductor substrate 9. The susceptor 8 is supported by a hollow shaft 10 connected to a driving member (not shown) and can be rotated by the driving member. Thus, the surface of the substrate 9 can react with gas while rotating at a constant rate, whereby a vapor-phase layer is formed at high yield.
A thermocouple 11 is inserted in the hollow shaft 10, for detecting the temperature of the susceptor 8. The temperature of the susceptor 8 is controlled by the output of the thermocouple 11. The elevator 4 is moved to adjust the position of the coil 3 such that the number of the windings of the coil 3, which surround that portion of the tube located above the substrate 9, is substantially equal to the number of the windings which surround that portion of the same located below the substrate 6. Further, the coil 3 is formed by a pipe through which water can flow to cool the coil.
The conventional vapor-phase growing apparatus, described above, has the following disadvantages:
The high-frequency generator 6 (frequency: 300 KHz; output: 10 KW) incorporated in the apparatus is very expensive, and requires a large space. Further, to install the generator 6, a special working is required: for example, a grounding rod must be embedded at a location remote from it.
Moreover, it is complex to put a semiconductor substrate in and out of the reaction tube 2 wound by the coil 3. That is, whenever the substrate 9 is put in or out of the reaction tube 2, the elevator 4 is moved up to remove the coil 3 from the reaction tube 2, and then the tube is removed from the housing 1. The substrate is then placed on the susceptor 8, the tube is again secured to the housing, and the elevator 4 is moved down to support the coil 3 in a desired position. The coil 3 must be positioned accurately; otherwise the thickness of the vapor-phase layer formed on the substrate 9 will vary.
In addition, since the reaction tube formed of quartz is easily broken, it is difficult to handle.